Chemical changes and reactions for 6.pptx

hi

1. GRADE: 6 SUBJECT: CHEMISTRY CHEMICAL CHANGES AND REACTIONS

2. Learning Objectives: SWBAT knowing chemical reactions involve substances, called reactants, interacting to form new substances, called products   Identify whether a chemical reaction has taken place through observations of the loss of reactants and/or the formation of products. Observe the different properties of the reactants (including evolving a gas, formation of a precipitate or change of colour) Use the particle model to describe chemical reactions.   Explain why a precipitate forms, in terms of a chemical reaction between soluble reactants forming at least one insoluble product.

3. What is a CHEMICAL REACTION?

4. What is a CHEMICAL REACTION? ​ All chemical reactions: Create new substance- The substances we end up with(PRODUCTS) are different from the ones you started with(REACTANTS) All chemical reactions are not reversible-you cannot  easily get  back the reactants .

5. Chemical reaction? Introduction to Chemical Reactions - YouTube

6. SIGNS/CHARACTERISTICS OF A CHEMICAL CHANGE

7. Evidence of a chemical reaction 7 Signs a Chemical Reaction is Taking Place - YouTube There are a number of signs that a chemical reaction is taking place. The big thing is that the atoms in a chemical reaction are rearrange and we end up with different substances. Remember that during chemical reactions there is a change in the energy and in the properties of the substance. These are things we can observe and measure.

8. PHYSICAL AND CHEMICAL CHANGES PHYSICAL CHANGE CHEMICAL CHANGE

9. CHEMICAL EQUATIONS

10. CHEMICAL EQUATIONS

11. COMBUSTION REACTIONS Burning is a chemical reaction. When a substance burns, it reacts with oxygen in the air.  Combustion refers to the process where a substance burns in the presence of Oxygen, giving off heat and light in the process. Examples of Combustion Burning of magnesium in the air An explosion of hydrogen in air Burning of Wax candle Combustion of petrol in a car’s engine Burning of natural gas in a bunsen burner A bush fire.

12. What is combustion? - YouTube Burning Magnesium Ribbon - YouTube Combustion Related Videos

13. Particle Model

14. C + O 2 CO 2

15. Strengths and limitations of PARTICLE model. Particle theory/model   helps to explain properties and behaviour of materials  by providing a model which enables us to visualise what is happening on a very small scale inside those materials.  The particle theory of matter is a model that describes the arrangement and movement of particles in a substance.  Simple to sketch Strengths

16. Limitations The particle theory assumes that particles are the same in all substances. However, particles in real life may be different from element to element in the following ways: mass or size/shape of the particles the force of attraction to other particles/space between the particles energy

17. Check for Understanding Explain how the particle diagram (given below)shows that a chemical change happens.

18. To begin with, iron particles are only joined to other iron particles, and sulfur particles are only joined to other sulfur particles. After the chemical change, iron particles and sulfur particles are joined to each other.

19. Reaction with water When a metal reacts with water, a metal hydroxide and hydrogen are formed. For example: Sodium reacts vigorously with water. sodium + water ➞ sodium hydroxide + hydrogen gas Calcium reacts readily with water. calcium + water ➞ calcium hydroxide + hydrogen  gas

20. Reaction of Alkali Metals with Water - YouTube

21. Reactions with acid

22. Change in energy:  Almost all chemical reactions involved energy change. Some chemical reactions produce heat while some take away heat. A change or reaction in which heat is released is called an  exothermic reaction. For example; In a reaction between carbon and oxygen, carbon dioxide is formed with the generation of heat. Carbon  +  Oxygen ------>Carbon dioxide + Heat

23. A change or reaction in which heat is absorbed from the surrounding is called an  endothermic reaction . For example in a reaction between carbon and sulphur, carbon disulphide is formed with the absorption of heat. Carbon + Sulphur + Heat---------> Carbon disulphide

24. Change in colour:  The colour of the product may differ from that of the reactants. For example; copper sulphate is blue in colour, but after reacting with iron, the product formed ( iron sulphate) is of green colour.

25. Reaction where carbon dioxide is evolved When baking powder and vinegar react, a gas is also given off. This gas is carbon dioxide. You can test for carbon dioxide by using limewater.When limewater mixes with the carbon dioxide, the limewater turns cloudy.

26. Reaction where Oxygen is evolved

27.   Tests for hydrogen, oxygen and carbon dioxide. Testing For Hydrogen, Oxygen, Carbon Dioxide & Chlorine | Matter | Chemistry | FuseSchool - YouTube Chlorine not included in the syllabus.

28. Test for hydrogen Hydrogen To test for hydrogen a small sample can be ignited. Hydrogen will make a squeaky pop when lit in air, care needs to be taken with this test as large amounts of hydrogen are very explosive in air.

29. Test for Oxygen Oxygen supports combustion so a good method of testing for oxygen is to take a glowing splint and place it in a sample of gas, if it re-ignites the gas is oxygen.

30. Test for Carbondioxide The best way of testing for Carbon dioxide is to bubble it through lime water. A positive test will result in the lime water turning milky. Lime water turns milky as the Calcium hydroxide (chemical name for limewater) reacts with carbon dioxide to form Calcium Carbonate which is insoluble in water and thus forms a milky white precipitate.

31. PRECIPITATE REACTIONS Precipitation reactions are such reactions in which two different soluble salts (which are in aqueous solutions) combine to form two products. One of these products is insoluble in the solution and is precipitated out (and is, therefore, referred to as the ‘precipitate’).

32. A precipitation reaction is when two aqueous solutions react to produce an insoluble compound. An insoluble compound is called the precipitate. To determine the products of a precipitate reaction, you simply change the partners of the reactants OR follow the formula below:

33. Examples of Precipitation Reactions

34. Extension-Precipitation Reactions For each of the precipitation reactions below write: a) The word equation b) The unbalanced chemical equation which must include the states of each compound.

35. What is a Neutralization Reaction? A neutralization reaction can be defined as  a chemical reaction in which an acid and base react together to form a salt and water as products.

36. In a neutralization reaction, there is a combination of H +  ions and OH –   ions which form water. A neutralisation reaction is generally an  acid-base   neutralization reaction.

37. Neutralisation in Everyday Life Indigestion Our stomach contains hydrochloric acid. It helps us to digest food. But too much of acid in the stomach causes indigestion. Sometimes indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide . It neutralises the effect of excessive acid.

38. Ant sting The sting of an ant contains formic acid. When an ant bites, it injects the acidic liquid into the skin. The effect of the sting can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.

39. Soil Treatment Excessive use of chemical fertilisers makes the soil acidic. Plants do not grow well when the soil is either too  acidic  or too  basic.  When the soil is too acidic, it is treated with bases like quick lime (calcium oxide ) or slaked lime calcium hydroxide . If the soil is basic, organic matter is added to it. Organic matter releases acids which neutralises the basic nature of the soil.

40. Factory Wastes The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, there fore, neutralised by adding basic substances.